Quadrant detectors are used in many applications, but their usefulness can be limited by their operating wavelength which is dependent on the semiconductor material which is used for the detector elements. For example, detectors operating at a laser wavelength of 1.064 μm tend to comprise silicon based materials which are used close to their long wavelength limit. It is also known to ‘extend’ the laser wavelength range of a silicon based detector by heating the detector to around 70° C. This ‘thermally’ reduces the band gap.
It will readily be understood from the above discussion that silicon based detectors cannot be extended to ‘eye safe’ laser wavelength of 1.5 μm as is now required, and other detector materials will need to be utilised, for example, Si:Ge, InGaAs and other Group III/V materials.
Furthermore, producing a detector to operate at two or more wavelengths simultaneously, for example, at 1.064 μm and 1.5 μm, will require specialised materials and devices, such as sandwich structures, which are inherently difficult and expensive to manufacture into quadrant geometries.